1. Field of the Invention
The present invention relates to an optical pickup, and more particularly to the configuration of an optical pickup having two separate optical systems that are selectively used according to the type of optical disc.
2. Description of Related Art
Conventionally, optical pickups are used to read information on an optical disc and write information on the optical disc. There are a plurality of types of optical discs such as a compact disc (CD), a digital versatile disc (DVD) and a blue-ray disc (BD). Thus, for convenience and the like, among conventional optical pickups, there are some optical pickups that can be compatible with a plurality of types of optical discs.
Among the optical pickups compatible with a plurality of types of optical discs, there are some optical pickups which have two separate optical systems that are selectively used according to the type of optical disc (for example, see patent documents 1 and 2). Here, the optical systems each function to guide light emitted from a light source to the information storage surface of the optical disc and to guide the light reflected off the information storage surface to a light receiving element. As a specific example of these optical pickups, there is an optical pickup in which one of the optical systems is used such as for reading information on a BD and in which the other optical system is used such as for reading information on a DVD or a CD.
Incidentally, in an optical pickup, an objective lens for condensing light emitted from a light source on the information storage surface of an optical disc is mounted on an objective lens actuator. This objective lens actuator can move the objective lens mounted at least in a focus direction and in a track direction. Here, the term “focus direction” refers to a direction that is perpendicular to the information storage surface of the optical disc; the term “track direction” refers to a direction that is parallel to a radial direction of the optical disc. The purpose of moving the objective lens in the focus direction is to control (perform focus control) the focal position of the objective lens such that the focal position is constantly located on the information storage surface. The purpose of moving the objective lens in the track direction is to control (perform track control) a light spot obtained by condensing light through the objective lens such that the light spot constantly follows the track of the optical disc.
Among the optical pickups having two separate optical systems, there are some optical pickups in which, as disclosed in, for example, patent documents 1 and 2, objective lenses included in the optical systems are mounted in one lens holder and in which one objective lens actuator allows the two objective lenses to move. With this configuration, for example, the size of a device and the number of components are advantageously reduced.
When two objective lenses are mounted in a lens holder, they are preferably mounted such that the space between the two objective lenses is minimized. This is because, for example, in an objective lens actuator that supports a lens holder with a wire, if the space between two objective lenses mounted in the lens holder is large, the drive sensitivity and the DC tilt of the objective lens actuator may be degraded, and this degradation is needed to be reduced.
When the space between two objective lenses is reduced, it is necessary to arrange upward reflecting mirrors included in two separate optical systems as close to each other as possible. The term “upward reflecting mirror” as used here refers to a mirror which reflects light such that the optical axis of light emitted from a light source is perpendicular to the information storage surface of an optical disc. Conventionally, one way to arrange the upward reflecting mirrors close to each other is to cut parts of the upward reflecting mirrors.
However, when the upward reflecting mirrors are cut, a cutting process is required, and thus the cost of the upward reflecting mirrors is increased. To overcome this problem, in patent document 1, there is provided a technology with which to reduce not only the cost of the mirrors but also the distance between the mirrors and which thus allows the distance between the objective lenses to be decreased.
To be sure, with the configuration of patent document 1, it is possible not only to reduce the cost of the mirrors but also to reduce the distance between the objective lenses with advantage. However, in view of the recent requirement to reduce the cost of an optical pickup, it is insufficient to reduce the cost of the mirrors, and it is necessary to achieve further cost reduction.
Patent document 1: JP-A-2007-334990
Patent document 2: JP-A-2008-59659